The invention relates to a method for forming an actuating variable to be produced periodic ally by a control unit in output periods for controlling an apparatus, in particular the ignition or fuel injection of internal combustion engines, in which output signals of at least two sensors are read into the control unit and based thereon individual components of the actuating variable are ascertained. Such a method is known from German Puiblished, Non-Prosecuted Application DE 40 04 516 A1.
In electronic engine control units for internal combustion engines, the actuating variables that are output, for example for the ignition angle or for the fuel injection quantity, are obtained from a plurality of individual components, which are calculated for measured values being furnished by various sensors, or are read out of memories associated with the measured values. Such calculation or readout processes are referred to below as xe2x80x9cdeterminationsxe2x80x9d.
In the case of the ignition, for instance, the engine rpm, the Pressure in the air intake conduit (separately for each cylinder and as a mean value for all of theucylinders, over two crankshaft rotations or a multiple thereof), the temperatures of the aspirated air and coolant or motor oil, the fuel quality, and the particular operating state of the engine, among other measured values, are utilized for such determinations.
The determination of the ignition angle, for instance, must meet the real-time requirements of the engine. In other words, the calculation of each ignition angle of all of the cylinders should include the current measured values. Since they are in fact analog values, they must be converted into digital variables before being read into the engine control unit.
The required sensor output signals must be read in and digitized each time between two ignitions in successive cylinders, or in other words during a one-half crankshaft rotation for a four-cylinder motor and a quarter rotation of the crankshaft for an eight-cylinder motor, each corresponding to one output period of the actuating variables or controlled variables, and in accordance with those measured values the individual components are determined (calculated or read out of a stored performance graph or table) and linked with the actuating variables.
In high-priced engines with many cylinders and microproces-sor-controlled control units having a number of sensors and calculation operations, the output period of the actuating variables is shorter at high engine rpm than the requisite determination time for the variables. The result is that the ignition angles, for instance, remain constant over a plurality of output periods or a plurality of ignitions, until a new value is present. In the high rpm range and in the case of simultaneous load dynamics (rapid surges of gas), that method causes engine-incompatible operating states, such as engine knocking, because the ignition timing is not current. In the control unit of German Published, Non-Prosecuted Application DE 40 04 516 A1, the intent is to solve the problem by providing additional microprocessors (controllers), which are supposed to process the read-in measured values parallel and independently of one another in different planes and with different priorities. Therefore a corresponding powerful processor-communications interface is needed. Such a construction is expensive and requires major effort and expense for hardware and software. It intrinsically involves a correspondingly high number of possible sources of error.
It is accordingly an object of the invention to provide a method for forming an actuating variable, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type, which makes do without additional hardware expense as compared with known embodiments and which nevertheless makes more-current actuating variables available for each output period in the high-rpm range.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a method for forming an actuating variable to be output periodically by a control unit in output periods for controlling an apparatus, in particular the ignition or fuel injection of internal combustion engines, which includes reading output signals of at least two sensors into the control unit and ascertaining individual components of the actuating variable based on the output signals, the improvement which comprises reading in the sensor output signals and determining the individual components periodically at intervals of one read-in period or one determination period being equal to or a multiple of the output period of the actuating variable; adjusting the read-in period of a sensor output signal to be dependent on a speed of variation of the sensor output signal, and in particular increasing the read-in period of the sensor output signal as the maximum speed of variation of the sensor output signal decreases; adjusting the determination period of each individual component to be dependent on the read-in periods of the sensor output signals involved in each individual component; and forming the actuating variable in each output period from all of the individual components with values being valid in that output period.
Accordingly, reading in of the sensor output signals is carried out as a function of their maximum variation speed, at different periodic intervals. At high rpm, for instance, signals which are read into the control unit are as follows:
xe2x80x9cengine rpmxe2x80x9d and xe2x80x9cpressure in air intake conduitxe2x80x9d (in a time slot of the aspiration stroke of each cylinder), which can vary quite quickly in every period;
xe2x80x9cengine temperaturexe2x80x9d and xe2x80x9caspirated air temperaturexe2x80x9d, which do not vary as fast, after every other or every fourth period; and
xe2x80x9cfuel qualityxe2x80x9d, which varies substantially at most after a gas tank filling operation, only after every eighth (or even more) period.
Furthermore, individual components, which are determined by using sensor output signals with a high maximum variation speed and which contribute substantially to forming the actuating variables, are determined at correspondingly shorter intervals (periods) than individual components which are determined by using sensor output signals with a lesser maximum variation speed and which accordingly undergo no variations or no serious variations (within the range of approximately 8 or 16 crankshaft rotations) or only slightly contribute to the value of the actuating variable.
In accordance with a concomitant mode of the invention, the read-in and determination periods, or their intervals, are dependent on the engine rpm.
In each output period, or accordingly during each half crankshaft revolution (180xc2x0 KW) for ignition systems of four-cylinder engines, a total ignition angle is formed from the individual components which are present (partial ignition angle amounts) and output.
In this way, with the same hardware expense, considerable savings of effort for reading, digitizing and computation can be attained, even though the actuating variables that are determined can be adapted substantially better to given operating conditions than in the case of known control units, because an updated actuating variable is available in every output period, or in other words for every ignition, even in the high-rpm range.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for forming an actuating variable, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.